C 2013 by I-Jen Lee. All Rights Reserved

c 2013 by I-Jen Lee. All rights reserved. UNDERSTANDING STAR FORMATION AT EARLY STAGES IN THE FILAMENTARY ERA BY I-JEN LEE DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Astronomy in the Graduate College of the University of Illinois at Urbana-Champaign, 2013 Urbana, Illinois Doctoral Committee: Associate Professor Leslie Looney, Chair Professor Emeritus Richard Crutcher Professor Telemachos Mouschovias Associate Professor Tony Wong Abstract This thesis presents a study of star formation at early stages in the filamentary era with a special focus on massive star and cluster formation. We first investigate the importance of filamentary structures in star formation and propose an observationally driven scenario for the evolution of filamentary structures from large-scale molecular clouds to small-scale circumstellar envelopes. In addition, as theories of star formation have gradually shifted from individual, isolated objects to the formation of clusters over the decade, we study the environment in the protocluster IRAS 05345+3157 to better understand the initial conditions for cluster formation. With CS(2-1) observations using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) ob- servatory, we have identified seven dense gas cores in this region and discussed the role of initial 8 3 turbulence. The gas cores require an external pressure of 10 K cm− to be bound to form possible seeds for future protostars. Furthermore, to understand massive star formation, we study the structure and kinematics of nine starless cores in Orion. As two main models about massive star formation, the turbulent core model and the competitive accretion model, predict different level of fragmentation in massive starless cores, our results from high angular resolution observations with CS(2-1) using CARMA show three to five fragments associated with each core, in a broad consistency with the models involving turbulent fragmentation. The number of fragments suggest that magnetic fields may be playing a role in suppressing the fragmentation. Also, the spectral data from the IRAM CS(2-1) observations of several cores show consistency with a picture of converging flows along a filament toward the core center; these flows may be important in massive and cluster formation. Our result does not fully support either the turbulent core scenario or the competitive accretion scenario. Finally, we present the first results from the CARMA Large Area Star Formation Survey (CLASSy) toward Serpens Main, NGC 1333, and Barnard 1. The project provides an unique ii opportunity to study cold, dense gas structure at millimeter wavelengths from 1500 AU to a few parsecs. The data reveal some exciting properties in morphological and kinematic structures for the first time, and will be unveiling more underlying physics in the star formation process in the future. iii To My Father and Mother. iv Acknowledgments I would like to express my greatest gratitute to my advisor Professor Leslie Looney. I thank Leslie for his restless discussions and insightful comments about science, useful and pleasant conversations, and numerous revisions on my proposals and papers. I thank Leslie for accepting me as his student, for helping making some sense of the confusion, and for allowing me to learn and grow at my own pace. I thank him for always responding quickly to paper drafts and emails even when he is in sabbatical. I thank him for being such a kind and honest person, so that I truely know when I have done a good or bad job. Finally, I thank him for his hospitality and generosity in preparing the yearly abundant dinner on Thanksgiving, and also to allow me to stay with his family when I visited NRAO, Charlottesville. The support and help I received from Leslie are beyond words, and are deeply appreciated. I would like to thank my thesis committee members, Professor Richard Crutcher, Professor Telemachos Mouschovias, and Professor Tony Wong, who offered guidance and support to this thesis. I appreciate their valuable comments and feedback throughout the years. I would also like to thank Professor You-Hua Chu, who admitted me to the graduate school which made this thesis possible. This thesis would not have been possible without the support of my collaborators. I would like to thank Doug Johnstone for turning an original scientific idea established in a conference to a research topic, which later became an enjoyable collaboration, and for all the theoretical insights from him throughout the collaboration. I would like to thank John Tobin, who always provides valuable comments and insights to all the projects/proposals we collaborate together. Thanks to John for always being a sounding board to my ideas and questions. I would like to thank Zhi-Yun Li, for useful discussions about turbulence and massive star formation, and for shaping up some of the paper drafts. Finally, many thanks to Randolf Klein, Scott Schnee, and Shiya Wang, for the v great support and help they offered to improve this thesis. I would to thank the LAI group at Illinois, who equipped me with the knowledge of interferom- etry. In particular, many thanks to Woojin Kwon, David Rebolledo, and Manuel Fernandez-Lopez, who are always willing to discuss and offering help when I have immediate research questions or confusions. I would like to thank CARMA for financial support. I would like to thank several people who have inspired me in different aspects about being a scientist along the way: Jin Koda, Fumi Egusa, Josh Dolence, Jonathan Seale, and Shiya Wang. I would not have accomplished this thesis without the love and support from dear family and friends. I would like to thank the friends from the Class 2007: Hotaka Shiokawa, David Rebolledo, Kuo-Chuan Pan, Nachiketa Chakraborty, and Yiran Wang, for being such terrific friends, for all the fun time and encouragements, and for being all together in ups and downs. I would like to thank Hsiang-Yi Yang, Amy Lien, Nick Indriolo, Rosie Chen, Ian Stephens, Nick Hakobian, Brett Hayes, and Hsin-Fang Chiang, for lighting up my days, and for their wonderful friendship. Also, I would like to thank Hsin-Yen Wang, Birdy Fong, Tito Tang, Pash Yang, and Tzu-Jung Lin, who care about me from the bottom of their hearts, and who are always there for me. Finally, I would like to thank my family, to whom this thesis is dedicated to. To my father, who educated me to pursue my own dreams and encouraged me to become who I want to be. To my mother, whose understanding and listening have been my strength to study abroad. To my grandmothers, whose encouragements always deeply warm my heart. To my siblings, for numerous fun conversations which release my stress. Finally, to my dear husband, Hotaka Shiokawa, for being such a wonderful person in the world who inspires me in every way, and for being my best friend in my life. Thank you for being never reluctant to show love and support, tenderness and kindness, encouragements and patience. Thank you for always being beside me through the years in happiness and difficulties, and for loving me as I am. And I thank God, for all of the above. vi Table of Contents ListofTables ........................................ ix ListofFigures........................................ x Chapter1 Introduction ................................ 1 1.1 Early Stages of Massive Star and Protocluster Formation ............... 2 1.1.1 ObservationalResults . ..... 2 1.1.2 Theory ....................................... 4 1.2 Star Formation in the Filamentary Era . .......... 5 1.3 OutlineoftheThesis.............................. ...... 5 Chapter 2 Filamentary Star Formation: Observing the Evolution toward Flat- tenedEnvelopes...................................... 7 2.1 Introduction.................................... ..... 7 2.2 Evolution of Protostellar Structure . ............ 9 2.2.1 Changing the Paradigm for the Inner Envelope of Class 0 Protostars . 9 2.2.2 Observationally-Driven Scenario for Filamentary Collapse ........... 11 2.3 SyntheticObservations. ........ 13 2.3.1 CARMAobservations ............................. 13 2.3.2 ALMAobservations .............................. 13 2.3.3 ModelingandResults ............................ 14 2.4 Conclusion ...................................... 16 Chapter 3 Massive Star-formation around IRAS 05345+3157: The Dense Gas . 29 3.1 Introduction.................................... ..... 29 3.2 Observations .................................... 31 3.2.1 CARMAobservations ............................. 31 3.3 Results......................................... 31 3.3.1 CSZerothMomentMapandSpectra . 31 3.3.2 MillimeterContinuumData . ..... 32 3.3.3 EstimatingtheCoreMass . 33 3.4 Discussion...................................... 37 3.4.1 ACollapsingCore ............................... 37 3.4.2 DynamicsofCores ............................... 39 3.4.3 Implication for Massive Star Formation . ......... 40 3.5 Summary ......................................... 42 vii Chapter 4 Earliest Stages of Protocluster Formation: Substructure and Kine- maticsofStarlessCoresinOrion . 50 4.1 Introduction.................................... ..... 50 4.2 Observations and Data Reduction . ........ 51 4.2.1 Thesample ..................................... 52 4.2.2 IRAM30-mobservations . 53 4.2.3 CARMAobservations ............................. 53 4.2.4 Herschel and JCMT archival data . ..... 54 4.3 Results and Data Analysis I: Morphology and Properties . ............... 54 4.3.1 IRAMmaps....................................

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